Coated superelastic stent

ABSTRACT

The coated superelastic stent is formed from a tube of collagen having an inner structure of a micro-cable made of strands of a material exhibiting super-elasticity or shape memory properties, such as nickel-titanium, and includes a strand of radiopaque material, such as platinum or gold, in order to provide a radiopaque marker during interventional therapeutic treatment or vascular surgery. The collagen tube can be loaded with a therapeutic agent for treatment of the desired site in the vasculature.

RELATED APPLICATIONS

[0001] This is a continuation in part of Ser. No. 08/986,004 filed Dec.5, 1997.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates generally to implantable devices forinterventional therapeutic treatment or vascular surgery, and moreparticularly concerns a coated superelastic stent formed from a strandedmicro-cable with enhanced radiopacity.

[0004] 2. Description of Related Art

[0005] The art and science of interventional therapy and surgery hascontinually progressed towards treatment of internal defects anddiseases by use of ever smaller incisions or access through thevasculature or body openings in order to reduce the trauma to tissuesurrounding the treatment site. One important aspect of such treatmentsinvolves the use of catheters to place therapeutic devices at atreatment site by access through the vasculature. Examples of suchprocedures include transluminal angioplasty, placement of stents toreinforce the walls of a blood vessel or the like and the use ofvasoocclusive devices to treat defects in the vasculature. There is aconstant drive by those practicing in the art to develop new and morecapable systems for such applications. When coupled with developments inbiological treatment capabilities, there is an expanding need fortechnologies that enhance the performance of interventional therapeuticdevices and systems.

[0006] One specific field of interventional therapy that has been ableto advantageously use recent developments in technology is the treatmentof neurovascular defects. More specifically, as smaller and more capablestructures and materials have been developed, treatment of vasculardefects in the human brain which were previously untreatable orrepresented unacceptable risks via conventional surgery have becomeamenable to treatment. One type of nonsurgical therapy that has becomeadvantageous for the treatment of defects in the neurovasculature hasbeen the placement by way of a catheter of vasoocclusive devices in adamaged portion of a vein or artery.

[0007] Vasoocclusion devices are therapeutic devices that are placedwithin the vasculature of the human body, typically via a catheter,either to block the flow of blood through a vessel making up thatportion of the vasculature through the formation of an embolus or toform such an embolus within an aneurysm stemming from the vessel. Thevasoocclusive devices can take a variety of configurations, and aregenerally formed of one or more elements that are larger in the deployedconfiguration than when they are within the delivery catheter prior toplacement. One widely used vasoocclusive device is a helical wire coilhaving a deployed configuration which may be dimensioned to engage thewalls of the vessels. One anatomically shaped vasoocclusive device thatforms itself into a shape of an anatomical cavity such as an aneurysmand is made of a preformed strand of flexible material that can be anickel-titanium alloy is known from U.S. Pat. No. 5,645,558, which isspecifically incorporated by reference herein.

[0008] The delivery of such vasoocclusive devices can be accomplished bya variety of means, including via a catheter in which the device ispushed through the catheter by a pusher to deploy the device. Thevasoocclusive devices, which can have a primary shape of a coil of wirethat is then formed into a more complex secondary shape, can be producedin such a way that they will pass through the lumen of a catheter in alinear shape and take on a complex shape as originally formed afterbeing deployed into the area of interest, such as an aneurysm. A varietyof detachment mechanisms to release the device from a pusher have beendeveloped and are known in the art.

[0009] For treatment of areas of the small diameter vasculature such asa small artery or vein in the brain, for example, and for treatment ofaneurysms and the like, micro-coils formed of very small diameter wireare used in order to restrict, reinforce, or to occlude such smalldiameter areas of the vasculature. A variety of materials have beensuggested for use in such micro-coils, including nickel-titanium alloys,copper, stainless steel, platinum, tungsten, various plastics or thelike, each of which offers certain benefits in various applications.Nickel-titanium alloys are particularly advantageous for the fabricationof such micro coils, in that they can have super-elastic or shape memoryproperties, and thus can be manufactured to easily fit into a linearportion of a catheter, but attain their originally formed, more complexshape when deployed. Although various materials are more or less kinkresistant when nickel-titanium alloys are dimensioned into wire smallerthan approximately 0.010 inches in diameter, they can have low yieldstrength and can kink more easily, thus severely limiting theapplications for such finely drawn wire in the fabrication ofvasoocclusive devices. As a further limitation to such applications,nickel-titanium alloys are also not radiopaque in small diameters, and asingle nickel-titanium wire would need to be approximately 0.012 inchesin diameter to be even slightly radiopaque. However, such a thickness ofa single nickel-titanium wire would unfortunately also be relativelystiff and possibly traumatic to the placement site, particularly if usedfor treatment of delicate and already damaged areas of the smalldiameter vasculature such as an aneurysm in an artery or vein in thebrain, for example.

[0010] One conventional guidewire for use in a catheter is known that ismade of a high elasticity nickel-titanium alloy, and is useful foraccessing peripheral or soft tissue targets. The distal tip of theguidewire is provided with a radiopaque flexible coil tip, and aradiopaque end cap is attached to the guidewire by a radiopaque ribbon.Such a construction is complex to manufacture, fragile and canpotentially break off during use with undesirable results. A stretchresistant vasoocclusive coil is also known that can be made of a primaryhelically wound coil of platinum wire, with a stretch-resisting wireattached within the primary coil between two end caps. Unfortunately,such a construction is relatively difficult to fabricate and alsofragile, allowing for the possibility of the fracture of the centralradiopaque wire, the coil, the welds or some combination of them, and itcan also potentially break off during use. Also, such a construction hasa complex and nonlinear bending characteristic, dependent on the spacingof the coils and central wire and the radius of the bend of the coil.

[0011] Stents are typically implanted within a vessel in a contractedstate and expanded when in place in the vessel in order to maintainpatency of the vessel, and such stents are typically implanted bymounting the stent on a balloon portion of a balloon catheter,positioning the stent in a body lumen, and expanding the stent to anexpanded state by inflating the balloon. The balloon is then deflatedand removed, leaving the stent in place. However, the placement,inflation and deflation of a balloon catheter is a complicated procedurethat involves additional risks beyond the implantation of the stent, sothat it would be desirable to provide a stent that can be more simplyplaced in the site to be treated in a compressed state, and expanded toleave the stent in place.

[0012] Stents also commonly have a metallic structure to provide thestrength required to function as a stent, but typically do not providefor the delivery of localized therapeutic pharmacological treatment of avessel at the location being treated with the stent. Stents formed ofpolymeric materials capable of absorbing and releasing therapeuticagents may not provide adequate structural and mechanical requirementsfor a stent, especially when the polymeric materials are loaded with adrug, since drug loading of a polymeric material can significantlyaffect the structural and mechanical properties of the polymericmaterial. Since it is frequently desirable to be able to providelocalized therapeutic pharmacological treatment of a vessel at thelocation being treated with the stent, it would be desirable to combinesuch polymeric materials with a stent structure to provide the stentwith the capability of absorbing and delivering therapeutic drugs orother agents at a specific site in the vasculature to be treated.

[0013] Conventional forms of stents are known that have a covering orouter layers of collagen, that can be used for enhancingbiocompatability and for drug delivery. One known tubular metal stent,for example, is combined with a covering sleeve of collagen in order toincrease the biocompatibility of the stent upon implantation. Thecollagen sleeve may be collagen per se or a collagen carried on asupport of Dacron or a similar material. Another three-layer type ofvascular prosthesis has two outer layers formed of collagen, and amiddle layer made from inert fibers such as synthetic fibers. Anothertubular reinforcing structure for use as a cardiovascular graft is madeof collagenous tissue with a reinforcing fibrous structure surroundingthe lumen. One drug delivery collagen-impregnated synthetic vasculargraft is also known, formed from a porous synthetic material havingcollagen such that the graft substrate cross-links the collagen in orderto render the substrate blood-tight. A matrix is also provided inanother biodegradable drug delivery vascular stent that is made fromcollagen or other connective proteins or natural materials that can besaturated with drugs. However, none of these types of stents provide fora coated, superelastic shape memory stent that can be delivered andreleased at the site in the vasculature to be treated in a compressedstate, and expanded to leave the stent in place without the need forplacement with a balloon catheter.

[0014] From the above, it can be seen that vasoocclusive devices andstents provide important improvements in the treatment of thevasculature. However, it would be desirable to provide a structuralelement that used to form a coated stent, that offers the advantages ofa shape memory alloy such as a nickel-titanium alloy, and thatincorporates radiopaque material in a stable configuration that is notsubject to breaking during use of the device, so that the device can bevisualized under fluoroscopy. The present invention meets these andother needs.

SUMMARY OF THE INVENTION

[0015] Significant advances have been made in the treatment ofneurovascular defects without resolution to surgery. More specifically,micro catheters have been developed which allow the placement ofvasoocclusive devices in an area of the vasculature which has beendamaged. In presently used techniques, the vasoocclusive devices takethe form of spiral wound wires that can take more complex threedimensional shapes as they are inserted into the area to be treated. Byusing materials that are highly flexible, or even super-elastic andrelatively small in diameter, the wires can be installed in amicro-catheter in a relatively linear configuration and assume a morecomplex shape as it is forced from the distal end of the catheter.

[0016] In order to gain the advantages presently being realized withmicro-catheter therapies and procedures to repair damage to thevasculature in the brain and other vessels, shape memory materials suchas nickel-titanium alloys have been incorporated in vasoocclusivedevices to be placed by the catheters. However, the range of diametersof wire and the configurations of the resulting geometry of both thecoils and the devices developed which can be used have been limited byboth the relatively small diameter of wire that must be used to avoidtrauma and allow housing within the catheter prior to deployment, andthe requirement for larger diameters to provide for radiopaque markersand mechanical robustness. In many cases this has resulted in primarywire characteristics in the coil that are unacceptably stiff, verydelicate, or subject to kinking. The present invention obtainssignificant advantages over such prior art devices by providing a cableof multiple strands of an alloy adapted to be used in catheters, stents,vasoocclusive devices, guidewires and the like, thus providing a kinkresistant, high strength material with highly desirable performancecharacteristics which can be altered by construction details to suit avariety of interventional therapeutic procedures.

[0017] More specifically, it has been found that single strands of smalldiameter nickel-titanium alloys, as well as other metal alloys, used toform vasoocclusive devices can be kinked if twisted and pulled as canoccur during or after deployment from a catheter, especially if thedoctor wishes to withdraw a partially deployed coil because it issomehow incorrect in size, shape or length to repair the damage to thevessel. Also, single wire coils are more likely to cause trauma to thearea to be treated if the wire is of a sufficient diameter to provideadequate tensile strength. Furthermore, such small diameter wires ofsome of these materials such as nickel-titanium, stainless steel and thelike, are not generally radiopaque with currently available equipment,necessitating the use of radiopaque markers attached to the device, withthe resultant possible diminution of functionality and increaseddiameter.

[0018] The present invention solves these and other problems byproviding, in its broadest aspect, a superelastic collagen coated stentformed from a micro-cable which includes at least one radiopaque strandto offer a continuous indication under fluoroscopy of the deployedconfiguration of the device incorporating the micro-cable. When combinedwith the benefits of a material such as nickel-titanium in the otherstrands of the micro-cable, numerous advantages are available from theuse of this basic construction in interventional medicine. The shape ofthe superelastic collagen coated stent can contour to the shape of theanatomical cavity or portion of the vasculature, and the superelasticcollagen coated stent would provide an adequate surface area of collagenfor contact with a vessel wall to deliver drugs to the vessel wall.

[0019] Briefly, and in general terms, a presently preferred embodimentof the present invention provides for a superelastic collagen coatedstent formed from a multi-stranded micro-cable made of a suitablematerial such as stainless steel or a nickel-titanium alloy, with thecable including at least one radiopaque strand, made of platinum,tungsten or gold, in order to serve as a marker during a procedure. Themulti-stranded micro-cable can be configured into a stent to reinforceareas of the small diameter vasculature such as an artery or vein in thebrain, for example. The superelastic collagen coated stent can be formedas a helical ribbon or tape, supported internally by a superelasticstructure that can be compressed along the width and length of the stentstructure, to be pushed by a pusher member through a microcatheter orcannula. When deployed in a helical configuration, with a ribboncross-section, a closed helical pitch is achieved, providing a collagentube in contact with the vessel wall. The stent is detachable from thepusher member. The superelastic collagen coated stent can bemanufactured by producing the superelastic inner structure, compressingthe structure, sliding it into a collagen tube, and allowing thesuperelastic inner structure to expand and flatten the tube into aribbon. The collagen tube of the superelastic collagen coated stent ispreferably loaded with a therapeutic agent or drug to reduce or preventrestenosis and thrombosis in the vessel being treated.

[0020] In one presently preferred embodiment, the invention accordinglyprovides for a superelastic collagen coated stent formed from amulti-stranded micro-cable having a plurality of flexible strands of asuper elastic material, and at least one radiopaque strand. In onepresently preferred embodiment, the multi-stranded micro-cable comprisesa plurality of flexible strands of nickel-titanium alloy, themicro-cable having at least one central axially disposed radiopaquewire, such as platinum, tungsten or gold, for example, in order toprovide a radiopaque marker during vascular procedures. In thispreferred embodiment, the construction of the invention places thelowest tensile strength and highest flexibility member, the radiopaquemarker strand, in a position in the cable which results in minimumstress on that member; at the same time, the superelastic material is inthe outer strands, which have the dominant affect on performanceparameters, thus enhancing the benefits of the material. Another benefitassociated with the invention compared to prior art devices is that themultiple stranded cable configuration, in addition to providing a highlyflexible and resilient structure, eliminates the necessity of a safetywire, since the failure of a single strand will not cause a severing ofthe cable. Also, the construction prevents stretching of the cable inthe event of failure of a single strand, which is a significant benefitcompared to constructions which have a coil around a central safetywire.

[0021] In a second presently preferred embodiment, the inventionincludes a superelastic collagen coated stent formed from a multistranded cable constructed of multiple twisted strands of a suitablematerial such as a shape memory alloy or super elastic alloy ofnickel-titanium, with one or more of the twisted strands consisting of aradiopaque material. The radiopaque strand may be one or more of theperipheral twisted strands and may also include one or more centralstrands of the cable. In a preferred aspect of the embodiment, the cableconsists of six peripheral twisted strands and a central linear corestrand, one or more of which can be of radiopaque material.

[0022] In a third aspect of the invention, the cable forming thesuperelastic collagen coated stent can be of linear strands that arearranged in a bundle and fastened or bound at intervals, orcontinuously, in order to maintain contact among the strands as thecable is bent. One or more of the strands may be radiopaque. Thisconstruction is adaptable to guidewires and other structures that mustbe pushable and/or torqueable, but still remain highly flexible andinclude radiopacity. Variations on this embodiment can include an outersheath which consists of a solid or helically wound cover to provideenhanced torqueability and pushability. More specifically, the outersheath can vary in thickness, stiffness of material or spring of thesheath members to provide desired variations in bending or stiffness ofthe cable. Such a construction is particularly adaptable to guidewiresand the like, and can be varied in terms of the binding or outer layerto alter the torqueability of the cable, and the flexibility of thecable can be varied along its length by the number and sizes of thestranded members in the cable.

[0023] In a fourth aspect of the invention, one or more of the strandsof the superelastic collagen coated stent can be of a therapeuticmaterial used to enhance treatment of the site after placement of thedevice. In one presently preferred embodiment of the invention, thecable includes twisted strands of wire around the periphery of thecable, at least one of which is radiopaque. The core of the cablecontains a therapeutic agent such as human growth hormone, geneticmaterial, antigens or the like that are intended to become active afterplacement. Such a construction can be adapted to a variety ofinterventional therapeutic treatments. In one aspect of this embodiment,one of the strands can have multiple functions, such as providing both atherapeutic effect and also contributing to the structural integrity ofthe cable. By using copper in such a micro-cable, for instance, thecopper can enhance the use of a device made from the cable as onintra-uterine device, with the copper also contributing to theradiopacity and structural integrity of the micro-cable. In the eventthat such an effect is desired, the therapeutic strand can be placed onthe exterior of the cable to enhance contact with the site to betreated.

[0024] These and other aspects and advantages of the invention willbecome apparent from the following detailed description and theaccompanying drawing, which illustrates by way of example the featuresof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 is a perspective of a radiopaque microstrand cableaccording to the invention.

[0026]FIG. 2 is a cross-section at 2-2 of FIG. 1.

[0027]FIG. 3 is a helical vasoocclusive coil formed of the cable of theinvention.

[0028]FIG. 4 is a spherical vasoocclusive structure formed using thecable of the invention.

[0029]FIG. 5 is a stacked coil vasoocclusive device formed using thecable of the invention.

[0030]FIG. 6 is a cross section of a vascular member with an aneurysmillustrating the approach of a vasoocclusive coil towards the aneurysm.

[0031]FIG. 7 is an illustration of a vasoocclusive coil which has beenintroduced into an aneurysm preparatory to being deployed within theaneurysm.

[0032]FIG. 8 is an illustration of a spherical vasoocclusive coil formedwith cable of the invention deployed within an aneurysm.

[0033]FIG. 9 is an alternate in a preferred embodiment of the inventionincluding a plurality of radiopaque strands within the cable.

[0034]FIG. 10 is an alternate preferred embodiment incorporating atherapeutic member within the radiopaque cable of the invention.

[0035]FIG. 11 is an alternate preferred embodiment of the presentinvention wherein strands of the cable are arranged within an exteriorbinding consisting of multiple straps about the cable.

[0036]FIG. 12 is a perspective view of the embodiment of FIG. 11.

[0037]FIG. 13 is an alternative embodiment to the embodiment of FIG. 12wherein the external binding of the cable represents a sheath woundabout the cable.

[0038]FIGS. 14a and 14 b are perspectives of alternative embodiments ofthe embodiment of FIG. 13.

[0039]FIG. 15 is a cross-section of an alternative embodiment in which aplurality of multi-strand cables are included within an external sheathsurrounding the cable.

[0040]FIG. 16 is a perspective view of the embodiment of FIG. 15.

[0041]FIG. 17 is a longitudinal sectional partial view of a flattenedribbon of a first embodiment of the superelastic collagen coated stentaccording to the principles of the invention.

[0042]FIG. 18A is a transverse sectional view of the flattened ribbon ofthe superelastic collagen coated stent taken along line 18-18 of FIG.17.

[0043]FIG. 18B is a transverse sectional view showing the compressedwidth of the flattened ribbon of the superelastic collagen coated stentof FIG. 18A.

[0044]FIG. 19 is a longitudinal sectional partial view of a flattenedribbon of a second embodiment of the superelastic collagen coated stentaccording to the principles of the invention.

[0045]FIG. 20A is a transverse sectional view of the flattened ribbon ofthe superelastic collagen coated stent taken along line 20-20 of FIG.19.

[0046]FIG. 20B is a transverse sectional view showing the compressedwidth of the flattened ribbon of the superelastic collagen coated stentof FIG. 20A.

[0047]FIG. 21 is a longitudinal sectional partial view of a flattenedribbon of a third embodiment of the superelastic collagen coated stentaccording to the principles of the invention.

[0048]FIG. 22A is a transverse sectional view of the flattened ribbon ofthe superelastic collagen coated stent taken along line 22-22 of FIG.21.

[0049]FIG. 22B is a transverse sectional view showing the compressedwidth of the flattened ribbon of the superelastic collagen coated stentof FIG. 22A.

[0050]FIG. 23 is a perspective view of a final form of a helicalsuperelastic collagen coated stent according to the principles of theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0051] While nickel-titanium alloys are useful in forming super-elasticor shape memory interventional devices, micro-coils formed of very smalldiameter wires of nickel-titanium alloy material for treatment of areasof the small diameter vasculature such as an artery or vein in thebrain, for treatment of aneurysms and the like, for example, can haverelatively low yield strengths and are somewhat subject to kinking, evenif made of super-elastic alloy. This can create problems if the coil isto be withdrawn after being emplaced by the doctor, as for instance, ifthe device is too small to effectively fill the cavity to be treated.Furthermore, even solid wires of a size suitable for use ininterventional devices are not very radiopaque.

[0052] While stents can be implanted within a vessel in a contractedstate and expanded when in place in the vessel in order to maintainpatency of the vessel, and typically have a metallic structure toprovide the strength required to function as a stent, metallic stentstypically do not provide for the delivery of localized therapeuticpharmacological treatment of a vessel at the location being treated withthe stent, and typically can not be delivered and released at the sitein the vasculature to be treated in a compressed state, and expanded toleave the stent in place without the need for placement of the stentwith a balloon catheter.

[0053] As is illustrated in the drawings, which are provided for thepurposes of illustration and not by way of limitation, the invention isembodied in a multi-stranded micro-cable formed of a plurality offlexible strands of a resilient material with the cable including atleast one radiopaque strand. In a presently preferred embodiment of theinvention illustrated in FIG. 1, the multi-stranded micro-cable 10 isapproximately from 0.0021 to 0.0045 inches in diameter, and comprises aplurality of flexible strands 12 of nickel-titanium alloy, with at leastone centrally, axially disposed radiopaque wire 14 which isapproximately from 0.0007 to 0.0015 inches in diameter. While the abovestated diameters represent those presently known to be compatible withthe invention, larger or smaller diameters may be useful for particularapplications. The central radiopaque wire 14 can be formed of platinumor gold, for example, or other similar suitable radiopaque metals, inorder to provide a radiopaque marker of the deployed configuration of adevice made of the cable during vascular surgery.

[0054] There are numerous benefits to the novel construction of theinvention for use in interventional devices and the like. By using thestranded or micro-cable construction of the invention, a device madefrom the micro-cable becomes virtually kink resistant compared to thesingle strand wires now commonly used in micro-coils. The multi-strandcable construction of the invention allows the micro-wires of the cableto slip across each other and reinforce each other rather than break ortake a set. Also, by incorporating a stranded radiopaque material suchas platinum, tungsten or gold into the cable construction, the device isradiopaque in sizes much smaller than with other constructions. Themicro-cable construction of the invention can be used to produce soft,kink resistant, radiopaque stents, guidewires, guidewire distal tips,and micro-coils.

[0055]FIG. 2 is a cross-section of the micro-cable of FIG. 1 at 2-2illustrating one presently preferred arrangement of the strands withinthe cable. In this embodiment, the exterior strands 12 are formed of aresilient material chosen to provide the characteristics desired for aspecific application in interventional therapies. In a presentlypreferred embodiment, this material is a nickel titanium super-elasticalloy which is heat treated such that the alloy is highly flexible at atemperature appropriate for introduction into the body via a catheter.By choosing such a material for micro-coils and the like, the devicesformed from the micro-cable can be relatively easily placed into theappropriate body cavity and after placement, the device will take on ashape designed to optimize the therapeutic purposes desired for thedevice. As illustrated in FIG. 2, such a cable can have a central core14 of a radiopaque material such as gold or platinum, thus dramaticallyenhancing the radiopacity of the cable. Even a solid super-elastic wireof the same diameter as the cable would have substantially lessradiopacity than the cable of the invention with the central gold orplatinum wire and the construction of the invention provides numerousother highly desirable characteristics. Among these characteristics isthe relative flexibility and resistance to kinking of the cable comparedto an equivalent single wire and substantially greater accommodation ofthe cable to bending, etc., with resultant lessening of trauma to thesurrounding tissue and ease of placement in a small body cavity.

[0056] One advantageous application of the invention is to vasoocclusivedevices formed of the micro-cable for insertion into aneurysms and othervascular defects for the purpose of occluding flow to the aneurysm. FIG.3 illustrates a helically wound coil 16 of micro-cable 10 which isformed to fit within a micro-catheter for insertion into an area uponwhich a therapeutic procedure is to be performed. While a helical coilis illustrated, it will be appreciated that numerous other secondaryshapes can be formed from the cable of the invention. More specifically,as illustrated in FIG. 4, a three dimensional, essentially spherical,device 18 can be formed of the cable 10, (or even of a coil of thecable, if appropriate) at a temperature sufficient to heat treat thematerial and thereby create a memory of the desired shape. The device isthen inserted into a catheter from which it may be deployed into ananeurysm or the like. The teachings of U.S. Pat. No. 5,645,558 describethe construction of such a device out of flexible wire and areincorporated by referenced herein. FIG. 5 illustrates a collapsed coilconfiguration 20 for a vasoocclusive device which also can be formedfrom the cable of the invention and is used for the purposes ofinsertion into aneurysms and other defects that have relatively largeentry necks compared to their internal volume.

[0057]FIG. 6 is an illustration of a catheter 22 using a coil 16 as avasoocclusive device made of the present invention and used forinsertion into an aneurysm 24 projecting laterally from a blood vessel26. The coil 16 is contained within the outer housing 28 of amicro-catheter that is used to house the coil prior to deployment. Theend of the catheter housing 28 is introduced into the opening 30 of theaneurism 24 by use of a guide wire (note shown). Thereafter, thevasoocclusive coil 16, and a pusher 32 are introduced into the catheterto provide for insertion of the vasoocclusive device into the aneurysm.In a presently preferred embodiment, the coil 16 formed of the cable ofthe invention is retained to an optical fiber pusher 32 which isattached to the coil by a collar of shape memory plastic material 34 asdescribed in co-pending application Ser. Nos. ______ the disclosure ofwhich are incorporated herein by reference. As shown in FIG. 7, the coilis introduced into the aneurysm and is then pushed from themicro-catheter until it fills the cavity.

[0058] Those skilled in the art will recognize that it is sometimes thecase that the vasoocclusive device must be withdrawn after it is fullyor partly inserted into the aneurysm. In such a case, there is a dangerthat the coil will be stretched beyond its elastic range or kink, orotherwise deform and make withdrawal difficult. Those skilled in the artwill also recognize that it is sometimes advantageous to formvasoocclusive devices of secondary shapes which are based upon a basicconfiguration of a coil or the like. The present invention includes suchapplications within the scope of the invention. However, whenvasoocclusive devices made of even super-elastic material are used, itis sometimes the case that the devices will be stretched or kinked whenwithdrawal is attempted. The cable of the present inventionsubstantially reduces the probability that kinking or stretching beyondyield will occur in a given instance, while at the same time providingradiopacity not available with other constructions. Thus, the presentinvention represents an important forward step in the technology ofinterventional therapy.

[0059] In one presently preferred embodiment, the shape memory collar 34is heated to a temperature which allows it to be shrunk onto coil 16.The collar is attached to optical fiber pusher 32 by an adhesive 36which retains high strength at temperatures beyond the shape memorymaterial transition point. After insertion, and when the operator issatisfied that the device is properly deployed, light energy from asource of coherent light is introduced into the proximal end of theoptimal fiber (not shown) and propagated in the distal end 38 of thefiber to cause the shape memory material collar 34 to return to itsprevious shape and release coil 16. Those skilled in the art willrecognize that the invention can also be used with a variety of otherplacement catheter systems, and it is not intended that the invention belimited to the placement concepts illustrated by way of example.

[0060] Those skilled in the art will recognize that a number of shapeddevices may be introduced into an area to be treated depending upon itsgeometry and the number of devices to be inserted. FIG. 8 illustrates anessentially spherical device 18 which has been deployed into such ananeurysm but it will commonly be found that a device such as that shownwould then be supplemented by a further coiled device inserted withinthe space inside the spherical device to completely occlude flow fromthe artery to the aneurysm.

[0061] While one presently preferred implementation of the micro-cableof the invention has been illustrated, those skilled in the art willappreciate that other variations of the invention may have advantagesfor certain purposes. FIG. 9 is an example of one such construction 40in which radiopacity is more desirable than in other forms and for thatreason a number of radiopaque strands 42, in this illustration four innumber, are formed into the cable along with three resilient materialstrands 44. It will also be appreciated that a larger or smaller numberof strands may be incorporated into a given cable and the cables may beformed of multiple cables in order to provide desired bending andstrength characteristics. It will also be appreciated by those skilledin the art that the invention is adaptable to the use of a variety ofmaterials which by themselves would not have been easily adaptable tomicro devices for interventional therapies. For instance, materials suchas copper are useful for intrauterine devices and the like, but copperwire, even when heavily alloyed, has certain limitations for use in suchdevices. By use of the present invention, composite cables incorporatingone or more strands of a desired material can be configured with otherstrands providing strength, flexibility, shape memory, super-elasticity,radiopacity or the like for previously unavailable characteristics inmicro devices.

[0062] The invention is also adaptable to numerous other purposes. FIG.10 illustrates a cross-section of a further preferred embodiment inwhich radiopaque strands 42 and resilient strands 44 form a portion ofthe cable and a therapeutic agent 48 is contained in one of the strands.Such a therapeutic agent can include human growth hormone, hydrogels, ora variety of other agents which will serve to provide desiredtherapeutic capabilities when placed within a specific area of the bodybeing treated by use of the micro-catheter. Depending upon theapplication of the therapeutic agent, its method of action and thedelay, if any, in the time after placement in which the therapeuticaction is desired, the agent strand may be placed in any of a variety ofpositions with the cable, from core wire outward. Also, it may bedesirable to coat one or more strands with a therapeutic material forcertain purposes. Such constructions are contemplated within the scopeof the invention.

[0063]FIG. 11 illustrates a cross-section of an additional presentlypreferred embodiment of the invention in which the strands 12, 14 of themicro-cable 10 are bundled and banded at intervals by bands 50 toproduce a composite banded cable 52 in order to provide increasedflexibility without unraveling or dislocation of the strands in thecable. FIG. 12 is a perspective view of the banded cable 50 of thisembodiment. While the illustrated configuration shows the strands beinglaid parallel within the cable, it is also possible in this constructionto include both twisted cables as the primary cables 10 within the outerbands 50 to form the composite cable 52. This configuration can use oneor more longitudinal strands 14 which are radiopaque, thus providing acontinuous indication of radiopacity within the cable. As a furtheralternative embodiment, it is possible for the longitudinal cable 52 tobe formed of a single inner cable 10 with bands 50.

[0064]FIG. 13 illustrates a further embodiment of the invention in whichlongitudinal strands of cables are contained within a wound cover 56 forthe purposes of providing a composite guide wire or the like 58 havingimproved torqueability. Such a construction has particular advantagesfor guidewire designs having improved radiopacity in very smalldiameters. It will be appreciated that in this configuration, as well asthe other longitudinally arranged multi-stranded cables, the number ofstrands and the degree to which they extend along the cable within thesheath is a variable which can be used to provide increased stiffness,pushability and torqueability in some sections with greater flexibilityin others. Additionally, composite cables according to the invention canincorporate additional elements normally not available in solid guidewires, such as optical, thermal or ultrasound imaging elements,therapeutic agent delivery catheters, and can take advantage ofmaterials which are not readily adaptable to prior art catheter or guidewire designs incorporating a primary wire structured element. FIGS. 14aand 14 b illustrate a further variable available because of theinvention; the exterior wrapped cover 56 can be wound at greater orlesser intervals 60 along the outside to provide variations in thetorqueability and stiffness of the composite cable. Also, the thicknessand width of the wrapping cover 56, as well as its material compositionalong the composite guide wire 58, can offer further capabilities forcustomizing the design for various applications. These advantages can becombined with the benefits of shape memory or super-elastic alloys tocreate guidewires and other devices with heretofore unavailablecapabilities.

[0065]FIG. 15 illustrates a cross-section of a micro-cable according tothe invention which has at least one overall exterior sheath to containthe micro-cable. The micro-cable may be made of one or more multiplestrand elements which may further include twisted or longitudinalstrands within their construction. The sheath may also be used tocontrol the torqueability characteristics of the cable and as discussedin co-pending application, Ser. No. ______, the sheath may bemulti-layered with different materials in order to provide a graduatedbending and stiffness characteristic over the length of the cable.

[0066] FIGS. 17 to 23 illustrate a superelastic collagen coated stentthat can advantageously be formed from one or more strands ormicro-cables of such strands as described above. The superelasticcollagen coated stent 70 can be compressed to a narrow thickness asillustrated in FIGS. 18B, 20B and 22B, and can be expanded at the siteto be treated to the form of the superelastic collagen coated stentribbon or tape forming a helical structure 72 illustrated in FIG. 23.The superelastic collagen coated stent comprises one or more groups offlexible strands 74 of superelastic, shape memory material, disposedwithin a tube 76 of collagen, forming a superelastic structure withinthe collagen tube that can be compressed along the width and length ofthe stent structure, to allow the stent structure to be pushed through amicrocatheter or cannula. Alternatively, the tube may also be made ofanother suitable material that is preferably biocompatible, and may be apolymer material such as a thermoplastic or elastomer, or other similarmaterials, for example, that preferably can be loaded with a therapeuticagent for treatment of the desired site in the vasculature. As isillustrated in FIG. 23, when deployed, in a helical configuration, witha ribbon cross-section, a closed pitch is achieved, providing a collagentube in contact with the vessel wall. The proximal end 78 of the stentpreferably includes a stem 80, grippable by a shape memory collar asdescribed above, to be detachable from a pusher member when delivered atthe site in the vasculature to be treated. The stent structure can bemanufactured by producing the inner superelastic structure, compressingthe structure, sliding it into a collagen tube, and allowing the innersuperelastic structure to expand and flatten the tube into a ribbon.

[0067] The collagen tube of the superelastic collagen coated stent ispreferably loaded with a therapeutic agent or drug, such as to reduce orprevent restenosis and thrombosis in the vessel being treated, forexample. The collagen tube of the superelastic collagen coated stent ispreferably loaded with a therapeutic agent or drug, such asantiplatelets, antithrombins, cytostatic and antiproliferative agentssuch as are well known in the art, for example, to reduce or preventrestenosis in the vessel being treated. While such therapeutic agentshave been used to prevent or treat restenosis and thrombosis, they areprovided by way of example and are not meant to be limiting, as othertherapeutic drugs may be developed which are equally applicable for usewith the present invention.

[0068] It will be apparent from the foregoing that while particularforms of the invention have been illustrated and described, variousmodifications can be made without departing from the spirit and scope ofthe invention. Accordingly, it is not intended that the invention belimited, except as by the appended claims.

What is claimed is:
 1. A superelastic collagen coated stent for use ininterventional therapy and vascular surgery, comprising in combination:a collagen tube; and a multi-stranded micro-cable disposed within saidcollagen tube, said multi-stranded micro-cable being formed from aplurality of flexible strands of a resilient material, said micro-cableincluding at least one radiopaque strand to provide a radiopaque marker.2. The superelastic collagen coated stent of claim 1 , wherein saidcombination of a collagen tube and a multi-stranded micro-cable forms aribbon forming the structure of said stent.
 3. The superelastic collagencoated stent of claim 1 , wherein said ribbon is configured to have ahelical shape.
 4. The superelastic collagen coated stent of claim 1 ,wherein said a multi-stranded micro-cable has a sinusoidal shape.
 5. Thesuperelastic collagen coated stent of claim 1 , comprising a pluralityof said multi-stranded micro-cables disposed within said collagen tube.6. The superelastic collagen coated stent of claim 1 , wherein said atleast one radiopaque strand comprises an axially disposed radiopaquewire.
 7. The superelastic collagen coated stent of claim 1 wherein saidplurality of flexible strands of a resilient material are comprised of asuper-elastic material.
 8. The superelastic collagen coated stent ofclaim 7 wherein said super-elastic material comprises a nickel titaniumalloy.
 9. The superelastic collagen coated stent of claim 1 wherein saidplurality of flexible strands of a resilient material are comprised of ashape memory material.
 10. The superelastic collagen coated stent ofclaim 9 wherein said shape memory material further comprises anickel-titanium alloy.
 11. The superelastic collagen coated stent ofclaim 9 wherein said shape memory material further comprises a shapememory polymer.
 12. The superelastic collagen coated stent of claim 1wherein said plurality of flexible strands further comprises a pluralityof flexible strands twisted about a central core wire, at least one ofsaid twisted strands comprising a radiopaque strand.
 13. Thesuperelastic collagen coated stent of claim 1 wherein said plurality offlexible strands further comprises a plurality of flexible strandstwisted about a central core wire, said central core wire being made ofa radiopaque material.
 14. The superelastic collagen coated stent ofclaim 1 wherein said radiopaque strand comprises a platinum strand. 15.The superelastic collagen coated stent of claim 1 wherein saidradiopaque strand comprises a gold strand.
 16. The superelastic collagencoated stent of claim 1 wherein said radiopaque strand comprises atungsten strand.
 17. The superelastic collagen coated stent of claim 9wherein said radiopaque strands comprise a plurality of strands of saidmicro-cable, at least one of said plurality of radiopaque strandsarrayed in the outer twisted strands of said cable.
 18. The superelasticcollagen coated stent of claim 1 , wherein said collagen tube is loadedwith a therapeutic agent.
 19. A superelastic collagen coated stent foruse in interventional therapy and vascular surgery, comprising incombination: a multi-stranded micro-cable disposed within said collagentube, said multi-stranded micro-cable being formed from a plurality offlexible strands of a resilient material, said micro-cable including atleast one radiopaque strand to provide a radiopaque marker; a sheath toconstrain said strands of said micro-cable about a longitudinal axis;and said multi-stranded micro-cable and sheath being disposed within acollagen tube.
 20. The superelastic collagen coated stent of claim 19wherein at least one of said strands comprises a shape memory material.21. The superelastic collagen coated stent of claim 19 wherein at leastone of said strands comprises a super-elastic material.
 22. Thesuperelastic collagen coated stent of claim 20 wherein said shape memorymaterial comprises a nickel titanium alloy.
 23. The superelasticcollagen coated stent of claim 21 wherein said superelastic materialcomprises a nickel titanium alloy.
 24. The superelastic collagen coatedstent of claim 19 wherein said sheath comprises a containment strandwound about said longitudinal strands.
 25. The superelastic collagencoated stent of claim 19 further comprising an outer flexible sheath oflow friction material.
 26. The superelastic collagen coated stent ofclaim 19 wherein said sheath comprises a heat shrinkable plastic tube.27. The superelastic collagen coated stent of claim 19 wherein saidplurality of flexible strands of a resilient material are comprised of asuper-elastic material.
 28. The superelastic collagen coated stent ofclaim 21 wherein said superelastic material comprises a nickel titaniumalloy.
 29. The superelastic collagen coated stent of claim 19 whereinsaid plurality of flexible strands of a resilient material are comprisedof a shape memory material.
 30. The superelastic collagen coated stentof claim 19 wherein said shape memory material further comprises anickel-titanium alloy.
 31. The superelastic collagen coated stent ofclaim 19 wherein said shape memory material further comprises a shapememory polymer.
 32. The superelastic collagen coated stent of claim 19wherein said radiopaque strand comprises a platinum strand.
 33. Thesuperelastic collagen coated stent of claim 19 wherein said radiopaquestrand comprises a gold strand.
 34. The superelastic collagen coatedstent of claim 19 wherein said radiopaque strand comprises a tungstenstrand.
 35. The superelastic collagen coated stent of claim 19 whereinsaid radiopaque strands comprise a plurality of strands of saidmicro-cable.
 36. The superelastic collagen coated stent of claim 19 ,wherein a plurality of flexible strands are twisted about a longitudinalaxis, at least one of said twisted strands being of a radiopaquematerial.